I can email you the service manual, no problem. Let me have an email address.
Most components are not very expensive (although some output devices can cost a bit) so its worth having a go but I would stress (not knowing your background so apologies if you are experienced) that there are lethal voltages inside the casing so I would say if you're not competent then leave well alone.
These are the sort of checks I would do to try and isolate where the problem was. Obviously do visual checks looking for burnt components, broken connections, bad tracks, dry joints etc.
Is there any hiss coming from the amp. Plug some headphones in (might be easier to hear than speakers) and see if there is any noise. It doesn't prove much if there isn't anything, but if there is hiss then it suggests the power amp section is running.
I would check the PSU section and check that the correct voltages are coming out in the right places. Obviously it is powering up but I would make sure all the voltages that should be coming out are there.
The preamp section looks as though it is on a separate board to the main poweramp section and here is a three wire connection between the two. Left Channel - Earth - Right Channel. I would send a signal into one of the inputs and put a scope on the output of the preamp section. If there is nothing then the preamp side of things is suspect. If there is a healthy output then it shows the preamp is up and so it narrows it down to psu/main amp.
There is a protection switch on the main board that disconnects the power amp output from the speaker terminals. I would again use a scope on the input side of the switch (poweramp output) just to make sure that there is no output as it's not likely to be a switch (but you never can take anything for granted)
From what I can see there are 5 fuse resistors on each channel of the poweramp section. They all need to be checked. They are FR483, FR487, FR491, FR489, FR485 on the left channel and FR484, FR488, FR492, FR490 and FR486 on the right.
I would then check all the transistors on each poweramp output section (12 per channel including a dual transistor) using the transistor tester (or diode) on a multimeter.
Hopefully I would by then have found something. If not, it's a case of testing more components and continuing troubleshooting.
Thats how I would approach it anyway. At the very least you will need a decent mutimeter and if possible a scope.
This obviously isn't exhaustive and people will have different methods but hopefully it gives you an insight as to what is involved.